Toll Grows From Mexican Swine Flu OutbreakAn outbreak of flu apparently caused by a pig virus has killed 57 and made hundreds sick around Mexico City. But is it related to a swine flu virus that has caused a handful of cases north of the border in California and Texas?

An outbreak of flu apparently caused by a pig virus has killed 57 and made hundreds sick around Mexico City. But is it related to a swine flu virus that has caused a handful of cases north of the border in California and Texas?

MICHELE NORRIS, host:

From NPR News this is ALL THINGS CONSIDERED. I'm Michele Norris.

Public health officials around the world are concerned about an outbreak of a new strain of flu in Mexico, one that seems to have originated in pigs. Today, officials there shut down schools; closed museums, libraries and theaters; and urged people to keep their distance from one another.

As NPR's Richard Knox reports, experts believe the same virus has also made its way to the Southwestern United States.

RICHARD KNOX: Just 24 hours ago, officials at the U.S. Centers for Disease Control and Prevention were trying to calm fears that seven cases of swine flu in California and Texas might be due to a dangerous new virus that could touch off a global pandemic. But acting CDC Director Richard Besser opened today's teleconference on a very different note.

Dr. RICHARD BESSER (Director, Centers for Disease Control and Prevention): Our concern has grown since yesterday in light of what we've learned since then.

KNOX: Most worrisome was new evidence from the CDC's Atlanta labs and others in Winnipeg, Canada, that the Mexican virus appears genetically very close, if not identical, to the one that's shown up north of the border.

Dr. BESSER: I think that you'd be safe in saying that. From everything we know to date, the virus appears to be the same.

KNOX: Experts think it's mainly a pig virus, but it also contains elements of flu viruses from birds and humans. One of the mysteries, though, is that the U.S. cases, now numbering eight, have involved relatively mild cases of flu. All eight have recovered, whereas Mexico, the World Health Organization says, has counted 859 cases of severe pneumonia and 62 deaths.

Besser notes that 400 million people cross the border between Mexico and the United States every year, but he says closing the border might not do much good.

Dr. BESSER: We are seeing cases in Texas, and we're seeing cases in San Diego, without any connection between them, which makes us think that there's been transmission from person-to-person through several cycles.

KNOX: That means the virus has already escaped from a small area that public officials could draw a ring around with containment measures such as closing the border.

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